1. Field of the Invention
The present invention relates to an optical head apparatus which records or reproduces data in or from an optical recording medium, such as an optical disk.
2. Description of Related Art
There is a great demand that an optical disk apparatus, as an outer storage device of a computer, for example, should be put into practical use or heightened its performance, because it has a large capacity and is capable of non-contact recording, reproducing, and the like. As compared with a magnetic disk apparatus that is widely known and used, the optical disk apparatus is inferior in its high-speed accessibility. However, if with a new type of the optical disk apparatus introduced, the inferior high-speed accessibility will be improved to be superior to the magnetic disk apparatus, in addition to its exchangeability with a recording medium, it will easily be understood that the optical disk apparatus is to replace the magnetic disk apparatus.
One type of improving the high-speed accessibility in the optical head apparatus is that a light source, a light-receiving unit, and the like are fixedly provided, and an actuator for objective lens, separately provided therein alone is made access with respect to a disk so that weight of a movable unit can be reduced. Naturally, in this actuator separation type, it is important to lighten the weight of the movable unit. During a high-speed access, the other type, that will be described later, of performing focusing control and tracking control for the disk by sliding or turning the movable unit around a pole hardly generates unnecessary vibration owing to unbalance and the like as compared with other types. So, this type is advantageous for the high-speed access.
FIG. 1 is a plan view to illustrate the optical head apparatus of prior art, FIG. 2 is a sectional view taken generally along the line II--II of FIG. 1, and FIG. 3 is a connection diagram of a tracking control coil of the optical head apparatus shown in FIG. 1. FIG. 2 also illustrates a disk that will be referred to later. In these figures, reference numeral 1 designates a moving body which is comprised of a base 2, a pole 3 mounted at right angles to the center of the base 2, a damper fixing pin 4 provided at both ends of the base 2, and a bearing 5 provided at four corners of the base 2.
Reference numeral 6 designates first moving means, which is comprised of a guide 7 made of iron being fit into the bearing 5, a linear motor coil 8 fixedly provided to both ends of the base 2 in FIG. 1 in a manner of surrounding the guide 7, a linear motor magnet 9 provided in parallel to the guide 7 and in proximity to the coil 8, and a linear motor yoke 10 provided adjacent to the magnet 9. Meanwhile, fine lines shown in the coil 8 designate the direction to which the coil 8 is rolled (each coil that will be referred to later is the same as this). And characters N and S shown in the magnet 9 designate polarities (each magnet that will be referred to later is the same as this). The guide 7, magnet 9, and yoke 10 are fixed to a fixed body (not shown) which is comprised of a frame body, a box body or the like, and the moving body 1 is guided by the guide 7 and is movable in the direction A. The guide 7 is connected to the yoke 10 in the upper and the lower portions of FIG. 1 (not shown).
Reference numeral 11 designates second moving means, which is comprised of a cylindrical focusing control yoke 12 with a circular ditch 13 being provided in the central portion of the base 2, a cylindrical focusing control magnet 14 provided at a side surface of the ditch 13, and a cylindrical focusing control coil 17 provided at the lower portion in FIG. 2 of a lens holder 15 that will be referred to later and in a position confronting the magnet 14 inside the ditch 13. There is provided the lens holder 15 around the pole 3 via a cylindrical movable bearing 16. The lens holder 15 is rotatable around the pole 3 in the direction B and is also slidable along the pole 3 in the direction C. Reference numeral 18 designates turning means, which is comprised of a tracking control magnet 19 provided to the base 2 above and below the lens holder 15 in FIG. 1, a tracking control yoke 20 provided to the base 2 being adjacent to the magnet 19, and a tracking control coil 21 provided in the lens holder 15.
The lens holder 15 is provided with a damper 22, which is locked by the damper fixing pin 4, generating a directional force of putting the lens holder 15 back to a neutral position when the lens holder 15 is shifted from the position. At one end of the lens holder 15, there is held an objective lens 23 whose optical axis is in parallel to the pole 3. And at the other end of the lens holder 15, there is provided a counter weight 24 which sustains balance between the lens holder 15 and the pole 3. On the base 2, below the objective lens 23 in FIG. 1 there is provided a reflecting mirror 25 which allows a light beam being incident in the direction D to reflect upon the objective lens 23. Above the pole 3 is positioned a disk 26 which is an optical recording medium. The center of the disk 26 is supported by the fixed body, and the disk 26 is adapted to rotate in a plane perpendicular to the optical axis of the objective lens 23.
Now will be described below the operation of the optical head apparatus of prior art. When data is recorded or reproduced, the disk 26 is rotated, and light beam emitted from a fixed optical system (not shown) including a light source becomes incident on the optical head apparatus in the direction of the arrow D and is reflected by the reflecting mirror 25, and, then, is turned 90 degrees, following which being focused on the disk 26 via the objective lens 23. While the access with respect to a desired track (not shown) on the disk 26 is performed, various kinds of control are done to allow the objective lens 23 to follow the disk 26 to cope with the surface deflection and decentering of the disk 26. Tracks on the disk 26 are provided above the objective lens 23 in a depth direction in FIG. 2. When it is desired to perform the access of the objective lens 23 with respect to the desired track, the linear motor coil 8 is energized. Because the coil 8 is located in a magnetic field of the linear motor magnet 9, a force is generated by energizing and the moving body 1 on which the coil 8 is mounted is moved in the direction A. There is no problem if the polarities N and S of the magnet 9 are opposite to those shown in the figure (the same as polarities of other magnets).
After that, fine adjustment is done for accurate tracking control against the decentering and the like of the disk 26. When a DC voltage V is applied to energize the tracking control coil 21 in a magnetic field of the tracking control magnet 19 as shown in the connection diagram of FIG. 3, couple of force in the direction of the arrow E, for example, is generated and then the lens holder 15 is rotated around the pole 3 against the force of the damper 22, moving the objective lens 23 in the direction B. In addition to this, adjustment of the position of the objective lens 23 is done in the direction C so that the light beam can correctly be focused in spite of the surface deflection and the like of the disk 26. To perform this focusing control, the focusing control coil 17 in a magnetic field of the focusing control magnet 14 is energized, and then a force acting in the direction C is generated to move the lens holder 15 on which the objective lens 23 is mounted.
Such an optical head apparatus of prior art has thus been constructed. As it is provided with the whole turning means 18 for tracking control on the moving body 1, weight of the movable unit including the moving body 1 and its loading members becomes larger. Accordingly, this larger weight becomes an obstacle to the high-speed access with respect to the disk 26.